1. Field of the Invention
The present invention relates generally to polyurea elastomers and, more specifically, to spray and reaction injection molded polyurea elastomers which exhibit a rapid dry time.
2. Description of Background Art
Elastomer systems are commonly recognized as, among other things, coating materials, with spray polyurea elastomer systems being particularly useful when employed in this capacity; rooftops and floorings are particularly well suited substrates. In addition to coating applications, spray polyurea elastomers are also employed in other open mold spraying applications for part production. Polyurea elastomers are also used for part production in closed mold applications, such as reaction injection molding (RIM) and reinforced reaction injection molding (RRIM).
In the case of part production, whether it be via open mold spraying, RIM or RRIM, one of the considerations confronting the skilled artisan is the dry time of the elastomer, i.e., the time it takes the molded part to dry. Specifically, a molded part fabricated from a polyurea elastomer which exhibits a slow dry time prohibits the worker from handling the molded work piece until it dries. A slow dry time will also upset the storage capability of the molded parts since, if they are stacked when they have not yet dried, the molded parts will invariably stick together. The resulting decrease in productivity becomes particularly problematic when molded parts are being produced and stored on a commercial level.
Similarly, in the case of coated substrates, such as floors and rooftops, a slow dry time prevents the coated surface from being walked on without resulting in surface defects, i.e., sticking, tracking, scratches, etc. Surface defects can also occur if the wet coating becomes exposed to adverse environmental elements.
In accordance with the present invention, the dry time of a polyurea elastomer is substantially reduced, thereby overcoming those shortcomings identified hereinabove.
U.S. Pat. No. 3,666,788 is directed to cyanoalkylated polyoxyalkylene polyamines which are specifically described as being useful as curing agents in polyurea coatings. Similarly, U.S. Pat. No. 3,714,128 describes cyanoalkylated polyoxyalkylene polyamines which are useful for slowing the gelling or hardening of the polyurea component so that good mixing of the isocyanate and amine components can be attained, which gives the sprayed material ample time to adhere and level before gelation of the polyurea coating occurs.
U.S. Pat. No. 3,979,364 describes the use of aminated polyethers as hereinafter used as a component with a polyol to make an elastomer.
U.S. Pat. Nos. 4,379,729; 4,444,910 and 4,433,067 describe elastomers which are prepared using a high molecular weight amine terminated polyether, an aromatic diamine chain extender and an aromatic polyisocyanate which may merely be polyisocyanate or a quasi-prepolymer prepared from a polyol reacted with a polyisocyanate wherein some isocyanate groups are still left unreacted. Various patents have been applied for and received using the basic combination recited above as well as various mold release agents and other additives, such as catalysts and fillers, including glass fibers. For example, see U.S. Pat. No. 4,607,090.
U.S. Pat. No. 4,585,850 describes a reaction injection molded (RIM) elastomer made by reacting, in a closed mold, an amine terminated polyether of greater than 1500 average molecular weight, having greater than 50 percent of their active hydrogens in the form of amine hydrogens; a chain extender; flaked glass pretreated with an amino silane coupling agent; and an aromatic polyisocyanate. The '850 patent referred to above contains a discussion of other applications and patents in the field; for example, U.S. Pat. Nos. 4,474,900 and 4,507,090.
U.S. Pat. No. 4,714,778 describes certain alkenylated toluene diamines which are reported as being useful as triand tetrafunctional chain extenders for forming polyurethane-urea elastomers.
U.S. Pat. No. 4,816,543 describes a monotertiary-alkyltoluene diamine which is reported as being useful as a chain extending agent for the formation of polyurethane-urea elastomers. At least 50 percent of the equivalent weight of the chain extending agent is mono-tertiary-butyltoluene diamine.
U.S. Pat. No. 4,806,615 describes reaction injection molded (RIM) elastomers consisting of a cured reaction product of primary or secondary amine terminated polyethers of greater than 1500 molecular weight, an aromatic polyisocyanate, a combination of a unsubstituted aromatic diamine chain extender and a substituted acyclic aliphatic diamine chain extender.
U.S. Pat. No. 4,218,543 describes the use of high molecular weight polyols, certain aromatic diamines and isocyanates for the production of RIM parts. This patent specifically claims as a chain extender 1-methyl-3,5-diethyl2,4-diaminobenzene (diethyltoluenediamine) and its isomer.
U.S. Pat. No. 4,523,004 discloses a substituted aromatic diamine chain extender in a RIM product.
U.S. Pat. No. 4,631,298 discloses blending various slower reacting chain extenders with diethyltoluene diamine in a RIM system using amine terminated polyethers.
Thus, it is our understanding that a polyurea elastomer which exhibits a rapid dry time as exhibited by the elastomer of the present invention has heretofore been unavailable.